The present invention relates to inspecting an object with penetrating radiation using both fan-shaped and pencil-shaped beams, which are scanned successively across the inspected object.
Penetrating radiation, such as X-rays, is often used for the inspection of enclosures such as cargo containers. The use of x-rays both transmitted through the inspected item and scattered by its contents is known in the art. Typically, the item is illuminated by a single source of x-rays, from which transmitted and scattered radiation are detected by detectors or arrays of detectors that are disposed, respectively, in the direction of propagation of the illuminating beam or in other directions, to the front, back, or sides of the inspected item.
U.S. Pat. No. 6,151,381, incorporated herein by reference, describes a penetrating radiation-based inspection system. A pencil-shaped beam of radiation is described for backscattered detection imaging. A fan-shaped beam of radiation is described for imaging the contents of an enclosure on the basis of radiation transmitted through the enclosure. Commonly assigned application Ser. No. 09/448,717 U.S. Pat. No. 6,192,104, describes such a system using a single source of radiation to produce non-coplanar pencil and fan beams.
A representative embodiment of the present invention includes an inspection system and method for inspecting an object with penetrating radiation. A source of penetrating radiation provides a beam of radiation. The beam alternates between a first beam shape and a second beam shape, the first and second beam shapes being coplanar. A first detector arrangement is for detecting penetrating radiation from a portion of the beam transmitted through the object and generating a transmitted radiation signal. A second detector arrangement is for detecting penetrating radiation from a portion of the beam scattered by the object and generating a scattered radiation signal. A processor determines at least one characteristic of the object based at least on the transmitted and scattered radiation signals.
The source of penetrating radiation may be an x-ray source, for example, a continuous or pulsed x-ray source from an x-ray tube. Alternatively, the source of penetrating radiation may be a linear accelerator. The beam shapes may be determined by a rotating chopper wheel, or by a rotating disk and slit arrangement. The first beam shape may be a pencil-shape, and the second beam shape may be a fan-shape. A collimator may be used for producing the fan shape. An absorber may reduce the intensity of low-energy components of the beam, while not significantly affecting the intensity of high-energy components of the beam. A scanner arrangement may be used for varying the orientation of the pencil shape with respect to the object. Either the object may be in motion with respect to the beam, or the system may be in motion with respect to the object.